A low-voltage domain powered digital microphone interface circuit with fully dynamic gain adjustment

Abstract

The present invention discloses a low-voltage domain powered, full-dynamic, gain-adjustable digital microphone interface circuit, comprising an audio analog front end and an analog-to-digital signal conversion circuit. The audio analog front end can improve the processing voltage domain, realize low-voltage domain power supply to process high-voltage domain signals, and simultaneously possess full dynamic and gain-adjustable characteristics. The power consumption level can be reduced by lowering the operating frequency. The analog-to-digital signal conversion circuit can realize full dynamic characteristics and adapt to the characteristics of the audio analog front end. At the same time, by introducing a residual feedback process, the conversion circuit has noise shaping characteristics, thereby improving the signal accuracy within the band. At the same time, the present invention adopts a dynamic amplifier, which can avoid the amplifier from working ineffectively for a long time in the standby stage, thereby maintaining the high energy efficiency characteristics of the system. Therefore, the present invention can simultaneously meet the low-voltage domain power supply requirements, higher processing signal dynamic range, high-precision quantization, high-energy-efficiency operation, and full dynamic characteristics.

Description

Technical Field

[0001] The present invention belongs to the technical field of CMOS analog integrated circuits, and in particular relates to a digital microphone interface circuit with full dynamic gain adjustment and powered by a low voltage domain. Background Art

[0002] A digital microphone interface circuit is a circuit that filters, amplifies, and processes analog signals containing voice information sent from a microphone sensor, converting them into digital signals. Because this analog-to-digital conversion is complete, its output is resistant to interference, and digital signals are more convenient to process in information technology equipment than analog signals. A digital microphone interface circuit generally consists of an audio analog front end for analog signal processing and an analog-to-digital converter for analog-to-digital conversion.

[0003] An analog front end (AFE) is an electronic device that amplifies small differential signals, provides driving capability, and suppresses common-mode noise. When processing relatively low-level analog signals, direct processing of the sensed analog signal, such as analog-to-digital conversion, can lead to numerous problems: input impedance mismatch leading to signal distortion; insufficient driving capability for the direct input signal, resulting in improper sampling in subsequent circuits; excessive common-mode noise; and low signal power, placing stringent requirements on the design of subsequent circuits. Therefore, audio analog front ends are widely used in modern electronic products as part of various sensor interface circuits.

[0004] An analog-to-digital converter (ADC) is an electronic device that converts analog signals into digital signals. Since most physical signals in nature exist in analog form, and computer systems excel at efficiently processing digital signals, specialized ADC components are essential for efficient analog signal processing. These circuits can convert analog capacitance signals, which are difficult for computers to process, into digital signals.

[0005] Conventional audio analog front-ends have the following drawbacks: ① Conventional audio analog front-ends are static components with static bias currents, making them unable to control whether to enable or disable them according to the needs of subsequent circuits, thus lacking low-power potential. ② The circuit's startup time is too long, requiring key nodes to be charged to the corresponding bias voltage before the circuit can operate normally. This drawback limits its potential for switching operating states. ③ The operating dynamic range of conventional audio analog front-ends is limited by the system supply voltage. As circuits move towards lower supply voltages, the operating range of audio analog front-ends will be limited. Reference [Zou L, Rocca G, De Blasi M, et al. Sigma-delta ADC based adaptive readout ASIC for digital audio sensor [J]. Analog Integrated Circuits and Signal Processing, 2017, 92: 383-392] points out that if this problem cannot be solved, severe harmonic distortion will be generated when processing high-dynamic-range input signals.

[0006] To overcome the above three defects, the conventional audio analog front-end is designed as a fully dynamic circuit that is not limited by the system power supply. On the one hand, it is necessary to change the conventional bias circuit design structure so that the entire circuit can work without an accurate bias current. On the other hand, it is necessary to design voltage domain amplification technology so that the main amplifier circuit part of the audio analog front-end can operate in a higher voltage domain, thereby solving the problem of completing high-level signal processing with low-voltage power supply. Summary of the Invention

[0007] In view of the above, the present invention provides a full-dynamic gain-adjustable digital microphone interface circuit powered by a low-voltage domain, which introduces a new circuit structure for application in the field of audio analog front-end and optimizes the conventional pipeline analog-to-digital converter structure. It has high-low voltage conversion and noise shaping characteristics, so that the system has the characteristics of full dynamics, voltage domain amplification, adjustable gain, and high-precision conversion.

[0008] A low-voltage domain powered digital microphone interface circuit with fully dynamic gain adjustable, comprising:

[0009] The audio analog front end with fully dynamic gain adjustment based on voltage domain multiplication technology is used to filter and amplify the external analog signal with voice information and then output a voltage signal with driving capability;

[0010] The analog-to-digital signal conversion circuit based on full-dynamic pipeline noise shaping is used to sample and process the voltage signal output by the audio analog front end, and then convert the voltage signal into a multi-bit digital signal; it adopts a two-stage pipeline structure. The first-stage coarse quantizer not only quantizes and amplifies the voltage signal but also performs the voltage regulation function, adjusting the voltage signal from the high voltage domain to the power supply voltage domain, facilitating the high-precision operation of the second-stage fine quantizer.

[0011] Furthermore, the audio analog front end includes:

[0012] The voltage domain multiplier circuit changes the series-parallel connection of the two internal power supply capacitors by controlling the switching signal provided by the logic circuit, outputting a supply voltage that exceeds the charging voltage value, thereby significantly increasing the output swing of the circuit;

[0013] an amplifier circuit connected to the voltage domain multiplication circuit via a pair of switches, controlling the on / off of the internal switch according to a switch signal provided by the control logic circuit, and amplifying the input analog signal containing voice information during the power supply phase of the voltage domain multiplication circuit;

[0014] The control logic circuit is used to provide corresponding switching signals to the voltage domain multiplication circuit and the amplifier circuit, and control the two circuits to realize power supply voltage multiplication and input signal amplification.

[0015] Furthermore, the voltage domain multiplication circuit includes five groups of switches K1 to K5 and two groups of power supply capacitor arrays, wherein one end of K1 is connected to the power supply voltage VDD, the other end of K1 is connected to one end of the first power supply capacitor array, one end of K2, and one end of K3, the other end of K2 is connected to one end of the second power supply capacitor array as the positive output end of the voltage domain multiplication circuit, the other end of the second power supply capacitor array is connected to the other end of K3 and one end of K5, the other end of K5 is connected to the other end of the first power supply capacitor array and one end of K4 as the negative output end of the voltage domain multiplication circuit, and the other end of K4 is connected to the power supply ground; the power supply capacitor array is composed of multiple switched capacitors connected in parallel, and the switched capacitor is composed of a capacitor and a switch connected in series; the on and off of the five groups of switches K1 to K5 are all controlled by switching signals provided by the control logic circuit.

[0016] Furthermore, the switch K2 adopts a high voltage domain switch, which includes two capacitors C1 and C2, three PMOS transistors P1 to P3 and five NMOS transistors N1 to N5, wherein the drain of N1 is connected to the drain of N2 and the source of P1 and is connected to the power supply voltage VDD, the source of N1 is connected to one end of C1 and the gate of N2, the source of N2 is connected to one end of C2, the gate of N1 and the source of P2, the drain of P1 is connected to the other end of C1 and the drain of N3, and the gate of P1 is connected to N The gate of C3 is connected to the other end of C2 and is connected to the switch control signal NCTRL, the source of N3 is grounded, the gate of P2 is connected to the gate of N4 and the gate of N5 and is connected to the switch control signal CTRL, the drain of P2 is connected to the drain of N4 and the gate of P3, the source of N4 is grounded, the drain of P3 is connected to the drain of N5 as one end of the high voltage domain switch, the source of P3 is connected to the source of N5 as the other end of the high voltage domain switch, and the switch control signal CTRL is complementary in phase to NCTRL.

[0017] The high-voltage domain switch will be closed during the charging stage of the audio analog front-end. At this time, the voltage amplification module is charged, and the switch control module will connect the two ports of the switch; when entering the signal processing stage of the analog front-end, the switch will cut off the connection between the capacitor and the external power supply. At this time, the voltage output of the voltage amplification module to power the buffer will be higher than the system power supply voltage. The control signal is converted from low level to high level through the buffer. The high-level control signal acts on the gate of the P-type transistor of the switch control module. At this time, although the drain of the P-type transistor is connected to the voltage value twice the system power supply voltage output by the voltage domain amplification circuit, since the gate is also connected to the high level boosted by the voltage amplification module, the gate-drain potential difference of the P-type transistor can still be maintained close to 0. The P-type transistor is in the cut-off state at this time. The switch with this structure can achieve a better shutdown effect under the condition of voltage domain amplification.

[0018] Furthermore, the amplifier circuit includes four groups of switches K6 to K9, two groups of filter capacitor arrays, and two groups of inverter arrays for amplification, wherein one end of K6 is connected to the positive output end of the voltage domain multiplication circuit, the other end of K6 is connected to the power supply end of the first inverter array and the power supply end of the second inverter array, one end of K7 is connected to the negative output end of the voltage domain multiplication circuit, the other end of K7 is connected to the ground end of the first inverter array and the ground end of the second inverter array, the input end of the first inverter array is connected to the positive input analog signal, the output end of the first inverter array is connected to one end of the first filter capacitor array and one end of K8, the other end of K8 is connected to one end of K9 and connected to the common mode voltage, the other end of K9 is connected to one end of the second filter capacitor array and the output end of the second inverter array, and the input end of the second inverter array is connected to An analog signal is inverted and input, and the other end of the second filter capacitor array is connected to the other end of the first filter capacitor array and grounded; the filter capacitor array is composed of multiple switch capacitors connected in parallel, and the switch capacitor is composed of a capacitor and a switch connected in series; the inverter array is composed of multiple inverters connected in parallel, and the inverter includes a switch, a PMOS transistor, and an NMOS transistor, wherein one end of the switch is the power supply end of the inverter array, the other end of the switch is connected to the source of the PMOS transistor, the gate of the PMOS transistor is connected to the gate of the NMOS transistor, and is the input end of the inverter array; the drain of the PMOS transistor is connected to the drain of the NMOS transistor, and is the output end of the inverter array; the source of the NMOS transistor is the ground end of the inverter array; the on and off of the four groups of switches K6 to K9 and the switches in the inverter are all controlled by the switch signals provided by the control logic circuit.

[0019] Due to the inverter's limited linear range, the inverter array design allows the number of parallel inverter groups connected to the amplifier circuit to be adjusted by switching signals from a control logic circuit. Alternatively, the linear range can be adjusted by switching inverters with different width-to-length ratios, thereby changing the width of the transistors in the inverters. This improves the linearity of the amplifier circuit and keeps the total harmonic distortion of the audio interface circuit within an acceptable range. When the two inverter arrays are balanced, the gain ratio of their output and input voltages is proportional to the capacitance of the series-connected power supply capacitor array and the capacitance of the filter capacitor array. The switched capacitors in the power supply capacitor array and the filter capacitor array are controlled by the control logic circuit. Adjusting the ratio of these two capacitors enables gain adjustment of the audio analog front end.

[0020] Furthermore, the working process of the audio analog front end includes two stages: charging and signal processing. In the charging stage, the voltage domain multiplier circuit is controlled by the control logic circuit to adjust the connection relationship of two groups of capacitors with equal capacitance to parallel connection, and then charge them with an external power supply. In the signal processing stage, the voltage domain multiplier circuit is controlled by the control logic circuit to disconnect from the external power supply and change the connection relationship of the two groups of capacitors to series connection. At this time, the positive output end of the voltage domain multiplier circuit will output a voltage value close to twice the external power supply voltage, the switch between the voltage domain multiplier circuit and the amplifier circuit will be closed, and the voltage domain multiplier circuit will start to supply power to the amplifier circuit for signal processing.

[0021] The audio analog front end of the present invention adopts a fully dynamic circuit design. When there is no signal to control the operation of the audio analog front end, the amplifier circuit is in a standby state and basically consumes no static power. Compared with the static analog front end, this feature of the dynamic analog front end will improve the energy efficiency of the present invention; the inverter-based amplifier structure used is in an open-loop working state, which reduces the impact of the feedback loop on the input signal and maintains the high-impedance characteristics of the input end; the working mode of the amplifier circuit is oversampling, and the higher sampling rate can enable the audio analog front end module to obtain the signal-to-noise ratio benefit, and it is also suitable for the requirements of the noise shaping analog-to-digital converter in the subsequent link. Based on the traditional dynamic operational amplifier, the present invention introduces a passive filter array at the output end. Since the circuit is fully dynamic, there are a large number of switching devices and transistors whose working states change with the circuit's working stage. When each switching device is disconnected or the transistor exits the working range, the thermal noise generated by the device will be locked at the corresponding node where the device is located. For the output node, this part of the noise will interfere with the output signal. The passive filter array introduced in the present invention filters the thermal noise within the band, improving the overall signal-to-noise ratio. At the same time, since it is a passive system, it avoids the impact on energy efficiency.

[0022] Furthermore, the analog-to-digital signal conversion circuit includes:

[0023] The first-stage analog-to-digital conversion circuit performs coarse quantization on the voltage signal output by the audio analog front end according to the control signal provided by the digital-to-analog control module, and outputs the quantized residual voltage;

[0024] an inter-stage gain amplifier, used to amplify the residual voltage and send it to the next stage;

[0025] The second-stage analog-to-digital conversion circuit quantizes the amplified residual voltage according to the control signal provided by the digital-to-analog control module;

[0026] The digital-to-analog control module is used to provide corresponding control signals to the first-stage and second-stage analog-to-digital conversion circuits, controlling the two-stage circuits to complete the conversion of analog signals.

[0027] The first-stage analog-to-digital conversion circuit uses a conventional successive approximation architecture, comprising a pair of N-stage capacitor arrays and a comparator. The N-stage capacitor array charges and discharges the weighted capacitors based on control signals from the digital-to-analog control module, thereby changing the voltage at the comparator input. The comparator output is connected to the digital-to-analog control module. This signal is both part of the digital-to-analog conversion result and used to provide information to the digital-to-analog control module, enabling it to determine the next control signal for the weighted capacitors, thereby implementing the successive approximation operation. The first-stage analog-to-digital conversion circuit operates at the Nyquist sampling frequency, enabling low-power operation.

[0028] The second-stage analog-to-digital conversion circuit adopts a noise-shaping successive approximation structure and has a pair of N-stage capacitor arrays, a comparator, a dynamic open-loop amplifier, a feedback capacitor, and a residual capacitor array. The N-stage capacitor array can charge and discharge the weight capacitor according to the control signal provided by the digital-to-analog control module, thereby changing the voltage at the common end of the capacitor array. The voltage at the common end is sent to the comparator input through a feedback capacitor. The feedback capacitor is connected in parallel with the residual capacitor array. The digital-to-analog control module will control the residual capacitor connected in parallel with the feedback capacitor during each conversion through a control signal, sharing the charge carrying the residual information of the previous conversion to the feedback capacitor, so that a residual voltage appears on the feedback capacitor. Therefore, the comparator input will receive information about the difference between the current voltage at the common end of the capacitor array and the residual voltage of the feedback capacitor. The comparator output will be connected to the digital-to-analog control module. This signal is both part of the digital-to-analog conversion result and is used to provide information to the digital-to-analog control module so that it can determine the control signal for the weight capacitor at the next moment to achieve successive approximation operation. After the successive approximation operation is complete, the D / A control module activates the dynamic open-loop amplifier, amplifies the residual voltage, and feeds it back to the residual capacitor array for storage. The D / A control module also controls the location of the residual capacitors where the converted residual voltage is stored. The second-stage analog-to-digital conversion circuit incorporates a residual processing feedback loop, leveraging its noise shaping characteristics to achieve higher-precision conversion results.

[0029] The inverter-based amplifier structure can achieve full dynamic characteristics and maintain almost zero power consumption before receiving the start signal from the digital-to-analog control module. When the start signal from the digital-to-analog control module is received, the residual signal of the first-stage analog-to-digital conversion circuit will be amplified. Since its input end is the gate of the transistor, the input node is a high-impedance node, and the opening and closing of the circuit will not affect the residual signal of the first-stage analog-to-digital conversion circuit.

[0030] The audio analog front end designed by the present invention can improve the processing voltage domain, realize low-voltage domain power supply to process high-voltage domain signals, and at the same time have full dynamic and gain adjustable characteristics, and the power consumption level can be reduced by reducing the operating frequency; the noise shaping analog-to-digital signal conversion circuit designed by the present invention realizes full dynamic characteristics, can adapt to the characteristics of the audio analog front end, and at the same time, by introducing the residual feedback process, the conversion circuit has noise shaping characteristics, which improves the signal accuracy within the band; the main energy consumption of the two is mostly occupied by the operational amplifier, but because the present invention adopts a dynamic amplifier, it can avoid the long-term invalid work of the amplifier in the standby stage, and maintain the high energy efficiency characteristics of the system. Therefore, the present invention can simultaneously have the characteristics of low-voltage domain power supply requirements, higher processing signal dynamic range, high-precision quantization, high-energy-efficiency operation, and full dynamic. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a structural block diagram of the application system of the digital microphone interface circuit of the present invention.

[0032] Figure 2 The figure is a schematic diagram of the circuit structure of the audio analog front end of the present invention.

[0033] Figure 3 Schematic diagram of the structure of the analog-to-digital signal conversion circuit of the present invention.

[0034] Figure 4 Schematic diagram of the working process of the audio analog front end of the present invention.

[0035] Figure 5 Schematic diagram of the output potential difference change of the voltage domain multiplier circuit.

[0036] Figure 6 Schematic diagram of the structure of the high voltage domain switch.

[0037] Figure 7 Schematic diagram of the off-resistance simulation comparison of high-voltage domain switches.

[0038] Figure 8 This is a simulated spectrum diagram of the digital signal output by the circuit system of the present invention.

[0039] Figure 9 Schematic diagram of the simulation output results of the input overload point power signal when the voltage multiplication is turned on and not turned on (the overload point power is the overload point of the circuit when the voltage multiplication feature is turned on). DETAILED DESCRIPTION

[0040] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] The low-voltage domain powered fully dynamic gain adjustable digital microphone interface circuit of the present invention includes: an audio analog front end with fully dynamic gain adjustable with voltage domain multiplication technology and an analog-to-digital signal conversion circuit with full dynamic pipeline noise shaping. The audio analog front end filters, amplifies and outputs a voltage signal with driving capability for the external input analog signal with voice information; the analog-to-digital signal conversion circuit samples and processes the voltage signal output by the audio analog front end, and converts this voltage signal into a multi-bit digital signal. It adopts a two-stage pipeline structure. In addition to quantization and amplification, the first-stage coarse quantizer can also perform voltage regulation, adjusting the high-voltage domain signal input by the audio analog front end to the power supply voltage domain, thereby facilitating the high-precision operation of the second-stage fine quantizer.

[0042] (1) The audio analog front end includes a voltage domain multiplication circuit, an amplifier circuit, and a control logic circuit, among which:

[0043] The voltage domain multiplication circuit uses a switch control signal provided by a control logic circuit to change the series-parallel connection of two power supply capacitors. This circuit can output a supply voltage that exceeds the charging voltage value, significantly increasing the circuit's output swing. The voltage domain multiplication circuit includes a high-voltage domain switch and two sets of power supply capacitor arrays. The high-voltage domain switch consists of a voltage amplification module and a switch control module. The voltage amplification module outputs a voltage higher than the power supply domain when the switch needs to be disconnected. The switch control module is a conventional switch. The high voltage output of the voltage amplification module enables the switch control module to disconnect a circuit whose voltage domain upper limit is higher than the control signal voltage, while maintaining very low leakage current.

[0044] The amplifier circuit consists of two groups of inverter arrays, which are connected to the voltage domain multiplication circuit through a pair of switches. The on and off of the switches are controlled by the control signal provided by the control logic circuit, and the amplification processing of the input signal is completed during the power supply stage of the voltage domain multiplication circuit.

[0045] The control logic circuit can be implemented by a finite state machine, and its output signal is used to control the voltage domain multiplication circuit and the amplification circuit to achieve the circuit processing voltage domain multiplication and input signal amplification processing.

[0046] The working process of the audio analog front-end includes two stages: charging and signal processing. During the charging stage, the voltage domain multiplier circuit will be controlled by the control logic circuit, and the connection relationship of the two groups of capacitors with equal capacitance will be adjusted to a parallel relationship, and then charged with an external power supply. During the signal processing stage, the voltage domain multiplier circuit will be controlled by the control logic circuit, disconnected from the external power supply, and the connection relationship of the two groups of capacitors will be changed to a series relationship. At this time, the positive output end of the voltage domain multiplier circuit will output a voltage value close to twice the external power supply voltage. The switch between the voltage domain multiplier circuit and the amplifier circuit will be closed, and the voltage domain multiplier circuit will start to supply power to the amplifier circuit for signal processing.

[0047] The audio analog front end of the present invention utilizes voltage domain amplification technology. The voltage domain multiplication circuit designed using this technology allows the two power supply capacitors in the circuit to be charged by an external power supply during the charging phase of the audio analog front end, via the control signal output by the control logic circuit. According to the formula for capacitors in parallel, the equivalent parallel capacitance at this time is:

[0048] C p =2·S sup

[0049] Where: C p is the equivalent parallel capacitance, S sup This is the capacitance of the two power supply capacitors connected to the circuit at this time.

[0050] According to the capacitor charge calculation formula, the total charge on the capacitor is:

[0051] Q tot =C p ·V system =2·C sup ·V system

[0052] Where: V system The system supply voltage.

[0053] When the audio analog front-end enters the signal processing stage, the logic control circuit outputs a control signal to disconnect the voltage domain multiplication circuit from the external power supply. At the same time, the connection topology of the two power supply capacitors changes from a parallel relationship to a series relationship. The supply voltage is output by the top plate of one capacitor and the bottom plate of the other capacitor. At this time, the equivalent series capacitance is:

[0054]

[0055] Where: C s is the equivalent series capacitance.

[0056] When the upper plate of one power supply capacitor is connected to the lower plate of another power supply capacitor, the charges at the connection node are neutralized because the stored charges are of opposite types but the same amount. Therefore, the charge at the connection node is no longer present. Therefore, the charge of the entire series capacitor system becomes half of that when charged in parallel. According to the capacitor-voltage formula, the supply voltage output by the series capacitors is:

[0057]

[0058] As a result, the voltage domain multiplication circuit outputs a voltage twice the system supply voltage value to the amplifier circuit. In addition, the voltage domain multiplication circuit also uses a switch that can operate in the high voltage domain. The working process and principle of this switch are as follows: when the control logic circuit controls the voltage domain multiplication circuit to enter the charging stage, since the switch is connected to the external power supply and one of the power supply capacitor arrays, the switch is closed at this time, and the external power supply charges the power supply capacitor array through the switch. At the same time, the power supply in the voltage amplification module of the switch charges the amplification capacitor to the system voltage through a conductive transistor; when the control logic circuit controls the voltage domain multiplication circuit to enter the signal processing stage, the upper plate of the power supply capacitor outputs a voltage higher than the high level of all control signals. At this time, the function of the switch is to cut off the output node of the power supply capacitor and the external power supply. If only the system high level is used to control the P transistor in the switch to turn off, since the gate-source voltage is still less than zero at this time, the switch cannot be turned off properly, resulting in a high leakage of the power supply capacitor to the external power supply node. In the present invention, during the signal processing stage, the lower plate of the amplified capacitor of the voltage amplification module will be connected to the high level of the control signal. Since the upper plate node of the amplified capacitor is in a suspended state at this time, the potential difference of the capacitor will remain constant, that is, the upper plate of the capacitor will output a voltage higher than the system high level, and this voltage depends on the sum of the voltage charged into the capacitor during the charging stage and the high level of the control signal; the voltage output by the voltage amplification module is supplied to a buffer, and the buffer will convert the input control signal from the system high level to the high level after amplification by the voltage amplification module. At this time, a higher level control signal is input to the gate of the P-type transistor of the switch. Since the level of the control signal is close to the level of the upper plate of the power supply capacitor at this time, the absolute value of the gate-source voltage of the P-type transistor is close to zero, and this P-type transistor is better turned off.

[0059] The audio analog front-end of the present invention adopts a new circuit structure. Unlike conventional audio analog front-end circuits, the amplifier circuit in the audio analog front-end of the present invention adopts an inverter-based amplifier structure. Since the gate voltages of a pair of P-type transistors and N-type transistors in the inverter are the same, both are the input voltage of the same phase. In order to drive the inflow current (source-drain current of the P-type transistor) and the outflow current (source-drain current of the N-type transistor) of the inverter to be the same, the P-type transistors and N-type transistors will passively change the drain voltage, that is, the output node voltage of the structure. This voltage will be related to the input voltage, thereby completing signal processing. Because this operating principle is different from that of conventional audio analog front-ends, the transistors in this circuit structure do not need to be biased in the amplification region. Therefore, this circuit structure can operate without a DC bias condition. After the inverter obtains the power supply voltage, it will obtain a corresponding output signal at the output node based on the gate voltage input to the inverter. This feature enables the structure to be designed as a dynamic circuit.

[0060] The amplifier circuit uses an inverter-based amplifier structure that can achieve adjustable gain. The gain formula of this structure is as follows:

[0061]

[0062] Where: ΔV S is a voltage constant, n is a process-related constant, The thermal voltage is only related to temperature, C RES is the equivalent power supply capacitor size, C X is the equivalent load capacitance, including the passive filter capacitor in the circuit and the sampling capacitor of the subsequent circuit. From this formula, it can be seen that the gain coefficient of the amplifier circuit of this structure can be controlled by adjusting the ratio of the power supply capacitance to the load capacitance.

[0063] The amplifier structure based on the inverter, when it is disconnected from the voltage domain multiplication circuit, this part is completely suspended and consumes almost no energy; when it is connected to the voltage domain multiplication circuit, it will start to consume the energy stored in the power supply capacitor to perform signal processing; the energy consumption of the audio analog front end of this structure is mainly concentrated in the charging and discharging of the power supply capacitor, and after the capacitor is charged to the same level as the system power supply, the charging power consumption is no longer consumed. Therefore, when this circuit is turned off or the operating speed is reduced, it is equivalent to reducing the number of times the power supply capacitor is charged per unit time, thereby achieving a reduction in system power consumption. Compared with the conventional static audio analog front end, when the subsequent circuit is in the non-sampling stage, the static audio analog front end still needs to consume power for signal processing. This part of power consumption is not necessary for the entire system. Using the full-dynamic audio analog front end of the present invention, the operation of the amplifier circuit can be stopped when the subsequent circuit is in the non-sampling stage, and only the voltage domain multiplication circuit is charged and processed to standby for the next signal processing, saving this part of energy consumption, thereby adapting to low-power application scenarios.

[0064] (2) The analog-to-digital signal conversion circuit includes a first-stage analog-to-digital conversion circuit, an inter-stage gain amplifier, a second-stage analog-to-digital conversion circuit, and a digital-to-analog control module, wherein:

[0065] The first-stage analog-to-digital conversion circuit is controlled by the signal from the digital-to-analog control module, completes the coarse quantization of the signal, and sends the quantized residual voltage to the next stage for fine quantization.

[0066] After the first-stage analog-to-digital conversion circuit completes its work, the inter-stage gain amplifier amplifies the residual voltage of the first-stage circuit and sends it to the next stage.

[0067] The second-stage analog-to-digital conversion circuit is controlled by the signal of the digital-to-analog control module and quantizes the residual voltage after being amplified by the inter-stage gain module.

[0068] The digital-analog control module can be implemented through a finite state machine, and its output signal is used to control the first-stage analog-to-digital conversion circuit, the inter-stage gain amplifier circuit, the second-stage analog-to-digital conversion circuit, and control the full-dynamic pipeline noise shaping analog-to-digital signal conversion circuit to complete the conversion of the analog signal.

[0069] The feedback process in the second-stage analog-to-digital converter circuit is controlled by the digital-to-analog control module. This mainly involves the order in which the residual capacitors are connected to the feedback capacitors during each conversion. By controlling the residual capacitor connection method in this step, the quantization noise transfer function of the second-stage analog-to-digital converter can be made into:

[0070] NTF(z)=(1-z -1 ) n

[0071] Where n represents the feedback order of the design. A higher order can achieve greater accuracy gains through noise shaping, but at the expense of increased hardware overhead.

[0072] This transfer function shows that after the quantization noise passes through this stage of the converter, it is equivalent to a high-pass process, so the quantization noise power in the low-frequency band will be suppressed. On the other hand, the transfer function of the second stage for the signal is:

[0073] STF(z)=1

[0074] The second-stage analog-to-digital signal conversion circuit is an all-pass filter for the signal, so the signal within the entire bandwidth will not be affected by the residual feedback process.

[0075] Example

[0076] like Figure 1 As shown, the fully dynamic gain adjustable digital microphone interface circuit of this embodiment includes an audio analog front end and a pipelined analog-to-digital converter. The overall signal path of the system is as follows: the microphone sensor powered by an external power supply (independent of the power supply of the interface circuit) will generate different electrical signals on a pair of differential capacitors as the sound pressure of the audio signal changes. This pair of differential analog signals will be input into the digital microphone interface circuit, and the power supply of the digital microphone interface circuit comes from an external low-voltage domain; the input end of the digital microphone interface circuit will be biased by a resistor to achieve high-pass filtering at the front end to filter out signals below the lower limit of the audio signal frequency acceptable to the human ear (signals less than 20 Hz); the differential analog signal is filtered and amplified by the audio analog front end, and a pair of differential signals with driving capability are output. The signal is sampled by the pipelined analog-to-digital converter and quantized by the two-stage analog-to-digital converter. Finally, the digital signal is output to the subsequent circuit or sent to the software for processing.

[0077] like Figure 3As shown, the output of the audio analog front end will be sampled by the switched capacitor array of the first-stage analog-to-digital conversion circuit. The sampling voltage at this stage is amplified by the dynamic range brought by the voltage multiplication technology of the audio analog front end, so the signal dynamic range is still in the high voltage domain; the sampling voltage will be sent to the comparator for comparison, and the output of the comparator will be connected to the digital-to-analog control module for judgment, and the subsequent control logic will be output to switch the switched capacitor array to complete the voltage approximation and quantization; the first-stage residual signal is input to the inter-stage amplifier, and the digital-to-analog control module will control the operation of the inter-stage amplifier. The gain of the inter-stage amplifier is based on the upper limit of the residual voltage of the first-stage analog-to-digital conversion circuit. The design ensures that the dynamic range of the interstage amplifier's output signal is within the supply voltage domain. The amplified signal is sampled by the switched capacitor array of the second-stage analog-to-digital conversion circuit, so the dynamic range of the signal processed by the second-stage analog-to-digital conversion circuit is within the supply voltage domain. The digital-to-analog control module controls the connection of some capacitors in the residual capacitor array to the feedback capacitor, completing charge sharing and sending residual information to both ends of the feedback capacitor. The voltage sampled by the second-stage switched capacitor array passes through the feedback capacitor and is then sent to the comparator. Therefore, the voltage at the comparator is actually the potential difference between the sampled voltage and the feedback capacitor, that is, the residual voltage. The approximate quantization process is similar to that of the first-stage analog-to-digital conversion circuit. After quantization, the residual voltage is sent to the residual amplifier. At the same time, the digital-to-analog control module controls the activation of the residual amplifier, amplifying the residual voltage and feeding it back to the specified residual capacitor in the residual capacitor array, thus completing the quantization process.

[0078] Figure 2 and Figure 4 The figure shows the analog circuit part of the audio analog front end and the corresponding working process in this embodiment, wherein Φ CAP[N] , Φ INV[N] , Φ FILT[N] They are the number of power supply capacitors, the number of amplifying inverters, and the number of passive filter capacitors that control the operation of the access circuit. These three signals are multi-bit bus signals. CEL[N] is a multi-bit strobe control signal input to the control logic module from the outside. The control logic module will control Φ according to the content of this signal. CAP[N] , Φ INV[N] , Φ FILT[N] Whether these three signals are gated or not, the gated control signal will remain valid, and the non-gated control signal will remain invalid. When the circuit enters the charging stage under the control of the control logic circuit, Φ SUP The signal becomes valid, and the external power supply is supplied to the parallel power supply capacitor C through the closed switch. SUP1 and C SUP1 Charging is carried out. At this time, the upper limit of the potential difference that the power supply capacitor can reach is the potential difference of the external power supply. When the circuit is controlled by the control logic circuit and enters the signal processing stage, Φ SUP The signal becomes invalid, ΦFIA The signal becomes valid, and the two power supply capacitors are disconnected from the external power supply circuit, and the topological relationship of the capacitors becomes series. The series capacitor group supplies power to the inverter amplifier, and the output node of the inverter amplifier is connected to V CM Disconnect and start amplifying and filtering the input signal. The supply voltage of these two sets of inverters is the output voltage of the voltage multiplier circuit. The trend of this voltage changing with the working stage is as follows: Figure 5 The simulation results show that when entering the charging stage, the capacitor charge is consumed by the previous working cycle, so the potential difference of the parallel capacitors will decrease from below V SUP Start charging to V SUP Nearby; when entering the signal processing stage, since the two capacitors will change from parallel to series connection, the overall potential difference of the capacitor group will become 2·V SUP This potential difference is the voltage domain that the voltage multiplier circuit ultimately supplies to the amplifier, so it is possible to power a low-voltage domain and process high-voltage domain signals.

[0079] Figure 2 The high voltage domain switch indicated in FIG is used in this embodiment. Figure 6 The circuit structure shown is divided into a voltage amplification module, a buffer and a switch control module. There are two capacitors in the voltage control amplification. When the switch is logically closed, the external power supply will charge the capacitor through the transistor. When the switch is logically disconnected, the NCTRL signal becomes valid, so the voltage of the lower plate of the right-measured capacitor rises. However, since the transistor connected to the upper plate of the capacitor is disconnected, the node is a high-resistance node and the charge on the capacitor will not change. Therefore, the voltage of the node is raised to the sum of the power supply voltage and the logic high level of the digital signal. This voltage will drive the buffer to perform level conversion on the control signal, converting the low-level control signal into a high-level control signal. The control signal will be input into the switch control module. The switch control module can be composed of various types of switches. In this embodiment, it is the simplest transmission gate switch. The control signal output by the buffer will control the P-type transistor. PLUS and MINUS are the two ports of this switch. Since they are applied to the high voltage domain, there are voltage values ​​higher than the power supply voltage domain in these two nodes. If the gate control signal of the P-type transistor is the power supply voltage, the P-type transistor cannot be turned off at this time, and there will be leakage between PLUS and MINUS. However, in this embodiment, since the gate voltage of the P-type transistor has been raised by the buffer, the transistor can be turned off.

[0080] Figure 7The simulation results comparing the off-resistance of a high-voltage switch are shown. The dashed line represents a switch without a voltage amplification module, while the solid line represents a switch with one. The two curves are plotted against the logarithmic axis on the left. The dotted line represents the voltage change of the control signal. With reference to the right axis, a voltage of 1.5 volts indicates the switch is on, and a voltage of 0 indicates the switch is off. The voltage required to disconnect the switch is as high as 2.5 volts, meaning one side of the switch is at 2.5 volts. According to the simulation results, the off-resistance of the switch without the voltage amplification module is in the tens of kiloohms. With the voltage amplification module enabled, the off-resistance of the switch increases to tens of megohms to gigahertz. This comparison shows that the off-resistance of the switch of the present invention is increased by more than 10,000 times, making it suitable for use in high-voltage domains.

[0081] Figure 8 The figure shows the spectrum characteristics of this embodiment under normal operation. It can be seen that this embodiment can dynamically process noise, moving the noise within the effective bandwidth (20 to 20,000 Hz) outside the bandwidth. This characteristic is reflected in the figure as the power density above 100,000 Hz gradually increases, thereby achieving a higher signal-to-noise ratio for in-band information conversion and improving the accuracy of the converter to meet the requirements of digital microphone projects for high-precision analog signal processing.

[0082] Figure 9 The simulation results of a 4.8V input signal are shown, both with and without voltage multiplication technology enabled. Both circuits are powered by 1.5V. The solid line represents the spectrum of the output signal after voltage multiplication is enabled, while the dashed line represents the simulation result without voltage multiplication. The circuit without voltage multiplication exhibits higher harmonic distortion, exceeding 30%. However, with voltage multiplication enabled, the harmonics in the output decrease rapidly with increasing order, reaching a total harmonic distortion of only 6%. This demonstrates that the voltage multiplication technology of the present invention can effectively suppress harmonic distortion in high-level inputs even when powered by a low voltage.

[0083] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It is apparent that those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without requiring creative effort. Therefore, the present invention is not limited to the above embodiments. Any improvements or modifications made by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A low-voltage domain powered digital microphone interface circuit with full dynamic gain adjustment, characterized in that: include: The audio analog front end with fully dynamic gain adjustment based on voltage domain multiplication technology is used to filter and amplify the external analog signal with voice information and then output a voltage signal with driving capability; The analog-to-digital signal conversion circuit, based on a fully dynamic pipelined noise shaping approach, samples and processes the voltage signal output by the audio analog front end, converting it into a multi-bit digital signal. It employs a two-stage pipeline structure. The first-stage coarse quantizer not only quantizes and amplifies the voltage signal but also performs voltage regulation, adjusting the voltage signal from the high-voltage domain to the supply voltage domain, facilitating high-precision operation of the second-stage fine quantizer. The audio analog front end comprises: The voltage domain multiplier circuit changes the series-parallel connection of the two internal power supply capacitors by controlling the switch signal provided by the logic circuit, outputting a supply voltage that exceeds the charging voltage value, thereby increasing the output swing of the circuit; an amplifier circuit connected to the voltage domain multiplication circuit via a pair of switches, controlling the on / off of the internal switch according to a switch signal provided by the control logic circuit, and amplifying the input analog signal containing voice information during the power supply phase of the voltage domain multiplication circuit; The control logic circuit is used to provide corresponding switching signals to the voltage domain multiplication circuit and the amplifier circuit, controlling the two circuits to realize power supply voltage multiplication and input signal amplification processing; The voltage domain multiplication circuit includes five groups of switches K1-K5 and two groups of power supply capacitor arrays, wherein one end of K1 is connected to the power supply voltage VDD, the other end of K1 is connected to one end of the first power supply capacitor array, one end of K2, and one end of K3, the other end of K2 is connected to one end of the second power supply capacitor array to serve as the positive output end of the voltage domain multiplication circuit, the other end of the second power supply capacitor array is connected to the other end of K3 and one end of K5, the other end of K5 is connected to the other end of the first power supply capacitor array and one end of K4 to serve as the negative output end of the voltage domain multiplication circuit, and the other end of K4 is connected to the power supply ground; the power supply capacitor array is composed of multiple switched capacitors connected in parallel, and the switched capacitor is composed of a capacitor and a switch connected in series; the on and off of the five groups of switches K1-K5 are all controlled by switching signals provided by a control logic circuit.

2. The fully dynamic gain adjustable digital microphone interface circuit according to claim 1, characterized in that: The switch K2 is a high voltage domain switch, which includes two capacitors C1 and C2, three PMOS transistors P1 to P3, and five NMOS transistors N1 to N5. The drain of N1 is connected to the drain of N2 and the source of P1 and is connected to the power supply voltage VDD. The source of N1 is connected to one end of C1 and the gate of N2. The source of N2 is connected to one end of C2, the gate of N1, and the source of P2. The drain of P1 is connected to the other end of C1 and the drain of N3. The gate of P1 is connected to the gate of N3. The electrode of N3 is connected to the other end of C2 and is connected to the switch control signal NCTRL, the source of N3 is grounded, the gate of P2 is connected to the gate of N4 and the gate of N5 and is connected to the switch control signal CTRL, the drain of P2 is connected to the drain of N4 and the gate of P3, the source of N4 is grounded, the drain of P3 is connected to the drain of N5 as one end of the high voltage domain switch, the source of P3 is connected to the source of N5 as the other end of the high voltage domain switch, and the switch control signal CTRL is complementary in phase to NCTRL.

3. The fully dynamic gain adjustable digital microphone interface circuit according to claim 1, characterized in that: The amplifier circuit includes four groups of switches K6 to K9, two groups of filter capacitor arrays, and two groups of inverter arrays for amplification, wherein one end of K6 is connected to the positive output end of the voltage domain multiplication circuit, the other end of K6 is connected to the power supply end of the first inverter array and the power supply end of the second inverter array, one end of K7 is connected to the negative output end of the voltage domain multiplication circuit, the other end of K7 is connected to the ground end of the first inverter array and the ground end of the second inverter array, the input end of the first inverter array is connected to the positive input analog signal, the output end of the first inverter array is connected to one end of the first filter capacitor array and one end of K8, the other end of K8 is connected to one end of K9 and connected to the common mode voltage, the other end of K9 is connected to one end of the second filter capacitor array and the output end of the second inverter array, and the input end of the second inverter array is connected to the negative input analog signal. An analog signal is input, and the other end of the second filter capacitor array is connected to the other end of the first filter capacitor array and grounded; the filter capacitor array is composed of multiple switch capacitors connected in parallel, and the switch capacitor is composed of a capacitor and a switch connected in series; the inverter array is composed of multiple inverters connected in parallel, and the inverter includes a switch, a PMOS transistor, and an NMOS transistor, wherein one end of the switch is the power supply end of the inverter array, the other end of the switch is connected to the source of the PMOS transistor, the gate of the PMOS transistor is connected to the gate of the NMOS transistor, and is the input end of the inverter array; the drain of the PMOS transistor is connected to the drain of the NMOS transistor, and is the output end of the inverter array; the source of the NMOS transistor is the ground end of the inverter array; the on and off of the four groups of switches K6 to K9 and the switches in the inverter are all controlled by the switch signals provided by the control logic circuit.

4. The fully dynamic gain adjustable digital microphone interface circuit according to claim 1, wherein: The working process of the audio analog front end includes two stages: charging and signal processing. During the charging stage, the voltage domain multiplier circuit is controlled by the control logic circuit to adjust the connection relationship of two groups of capacitors with equal capacitance to parallel connection, and then charged by an external power supply. During the signal processing stage, the voltage domain multiplier circuit is controlled by the control logic circuit to disconnect from the external power supply and change the connection relationship of the two groups of capacitors to series connection. At this time, the positive output terminal of the voltage domain multiplier circuit will output a voltage value twice the external power supply voltage, the switch between the voltage domain multiplier circuit and the amplifier circuit will be closed, and the voltage domain multiplier circuit will start to supply power to the amplifier circuit for signal processing.

5. The fully dynamic gain adjustable digital microphone interface circuit according to claim 3, characterized in that: When the two inverter arrays are balanced, the gain ratio of their output and input voltages is proportional to the capacitance value of the power supply capacitor array connected in series and the capacitance value of the filter capacitor array. The switched capacitors in the power supply capacitor array and the filter capacitor array are controlled by a control logic circuit to adjust the proportional relationship between the two groups of capacitance values ​​to achieve gain adjustment of the audio analog front end.

6. The fully dynamic gain adjustable digital microphone interface circuit according to claim 1, characterized in that: The analog-to-digital signal conversion circuit includes: The first-stage analog-to-digital conversion circuit performs coarse quantization on the voltage signal output by the audio analog front end according to the control signal provided by the digital-to-analog control module, and outputs the quantized residual voltage; an inter-stage gain amplifier, used to amplify the residual voltage and send it to the next stage; The second-stage analog-to-digital conversion circuit quantizes the amplified residual voltage according to the control signal provided by the digital-to-analog control module; The digital-to-analog control module is used to provide corresponding control signals to the first-stage and second-stage analog-to-digital conversion circuits, controlling the two-stage circuits to complete the conversion of analog signals.

7. The fully dynamic gain adjustable digital microphone interface circuit according to claim 6, characterized in that: The first-stage analog-to-digital conversion circuit adopts a conventional successive approximation structure, the second-stage analog-to-digital conversion circuit adopts a noise-shaping successive approximation structure and adds a residual processing feedback link, and the digital-to-analog control module is implemented by a finite state machine.

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